AWS SecretsManager

This guide shows how to setup a KES server that uses AWS SecretsManager as a persistent key store protected by the AWS-KMS:

                         ╔═══════════════════════════════════════════════════╗
┌────────────┐           ║  ┌────────────┐          ┌─────────────────────┐  ║
│ KES Client ├───────────╫──┤ KES Server ├──────────┤ AWS Secrets-Manager │  ║
└────────────┘           ║  └────────────┘          └──────────┬──────────┘  ║
                         ╚═════════════════════════════════════╪═════════════╝
                                                               |
                                                         ┌─────┴─────┐
                                                         |  AWS-KMS  |
                                                         └───────────┘

---

AWS SecretsManager

The AWS SecretsManager is basically a key-value store for secrets - like passwords, access tokens and cryptographic keys. AWS will encrypt these secrets via their AWS-KMS service.

1. Create AWS Access/Secret KeyPair

To create, retrieve and delete secrets at/from the AWS SecretsManager you need an AWS IAM user - i.e. an AWS access key and AWS secret key pair with sufficient IAM policy permissions.

Go to the AWS console and create a new user. Use the Programmatic access type to create a new access key / secret key pair.

2. Create AWS Policy

Attach policies to that user to grant access to the AWS SecretsManager and the AWS-KMS. AWS has predefined policies (SecretsManagerReadWrite and AWSKeyManagementServicePowerUser) that will work but also grant a lot of permissions that are not needed. Your AWS IAM user needs to have to following permissions:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "Stmt1578498399136",
      "Action": [
        "secretsmanager:CreateSecret",
        "secretsmanager:DeleteSecret",
        "secretsmanager:GetSecretValue",
        "secretsmanager:ListSecrets"
      ],
      "Effect": "Allow",
      "Resource": "*"
    },
    {
      "Sid": "Stmt1578498562539",
      "Action": [
        "kms:Decrypt",
        "kms:DescribeKey",
        "kms:Encrypt"
      ],
      "Effect": "Allow",
      "Resource": "*"
    }
  ]
}

Note that this example policy grants access to all KMS and SecretsManager resources. You can restrict that by specifying a AWS ARN as resource instead *.

KES Server Setup

1. Generate KES Server Private Key & Certificate

First, we need to generate a TLS private key and certificate for our KES server. A KES server can only be run with TLS - since secure-by-default. Here we use self-signed certificates for simplicity.

The following command generates a new TLS private key (private.key) and a self-signed X.509 certificate (public.crt) issued for the IP 127.0.0.1 and DNS name localhost:

$ kes identity new --ip "127.0.0.1" localhost

  Private key:  private.key
  Certificate:  public.crt
  Identity:     2e897f99a779cf5dd147e58de0fe55a494f546f4dcae8bc9e5426d2b5cd35680

If you already have a TLS private key & certificate - e.g. from a WebPKI or internal CA - you can use them instead. Remember to adjust the tls config section later on.

2. Generate Client Credentials

The client application needs some credentials to access the KES server. The following command generates a new TLS private/public key pair:

$ kes identity new --key=client.key --cert=client.crt MyApp

  Private key:  client.key
  Certificate:  client.crt
  Identity:     02ef5321ca409dbc7b10e7e8ee44d1c3b91e4bf6e2198befdebee6312745267b

The identity 02ef5321ca409dbc7b10e7e8ee44d1c3b91e4bf6e2198befdebee6312745267b is an unique fingerprint of the public key in client.crt and you can re-compute it anytime:

$ kes identity of client.crt

  Identity:  02ef5321ca409dbc7b10e7e8ee44d1c3b91e4bf6e2198befdebee6312745267b

3. Configure KES Server

Next, we can create the KES server configuration file: config.yml. Please, make sure that the identity in the policy section matches your client.crt identity.

address: 0.0.0.0:7373 # Listen on all network interfaces on port 7373

admin:
  identity: disabled  # We disable the admin identity since we don't need it in this guide 
   
tls:
  key: private.key    # The KES server TLS private key
  cert: public.crt    # The KES server TLS certificate
   
policy:
  my-app: 
    allow:
    - /v1/key/create/my-key*
    - /v1/key/generate/my-key*
    - /v1/key/decrypt/my-key*
    identities:
    - 02ef5321ca409dbc7b10e7e8ee44d1c3b91e4bf6e2198befdebee6312745267b # Use the identity of your client.crt
   
keystore:
     aws:
       secretsmanager:
         endpoint: secretsmanager.us-east-2.amazonaws.com  # Use the SecretsManager in your region.
         region:   us-east-2                               # Use your region
         kmskey:   ""                                      # Your AWS-KMS master key (CMK) - optional.
         credentials:
           accesskey: "" # Your AWS Access Key
           secretkey: "" # Your AWS Secret Key

4. Start KES Server

Now, we can start a KES server instance:

$ kes server --config config.yml --auth off

On linux, KES can use the mlock syscall to prevent the OS from writing in-memory data to disk (swapping). This prevents leaking senstive data accidentality. The following command allows KES to use the mlock syscall without running with root privileges:

$ sudo setcap cap_ipc_lock=+ep $(readlink -f $(which kes))

Then, we can start a KES server instance with memory protection:

$ kes server --config config.yml --auth off --mlock

KES CLI Access

1. Set KES_SERVER Endpoint

The KES CLI needs to know to which server it should talk to:

$ export KES_SERVER=https://127.0.0.1:7373

2. Use Client Credentials

Further, the KES CLI needs some access credentials to talk to a KES server:

$ export KES_CLIENT_CERT=client.crt

$ export KES_CLIENT_KEY=client.key

3. Perform Operations

Now, we can perform any API operation that is allowed based on the policy we assigned above. For example we can create a key:

$ kes key create my-key-1

Then, we can use that key to generate a new data encryption key:

$ kes key dek my-key-1
{
  plaintext : UGgcVBgyQYwxKzve7UJNV5x8aTiPJFoR+s828reNjh0=
  ciphertext: eyJhZWFkIjoiQUVTLTI1Ni1HQ00tSE1BQy1TSEEtMjU2IiwiaWQiOiIxMTc1ZjJjNDMyMjNjNjNmNjY1MDk5ZDExNmU3Yzc4NCIsIml2IjoiVHBtbHpWTDh5a2t4VVREV1RSTU5Tdz09Iiwibm9uY2UiOiJkeGl0R3A3bFB6S21rTE5HIiwiYnl0ZXMiOiJaaWdobEZrTUFuVVBWSG0wZDhSYUNBY3pnRWRsQzJqWFhCK1YxaWl2MXdnYjhBRytuTWx0Y3BGK0RtV1VoNkZaIn0=
}